In the capillary electrophoresis method, ions that have gathered on the inner wall of a capillary tube are transferred upon voltage application to generate an electroosmotic flow, which transfers the sample, and thus electrophoresis is performed. For the capillary tube, one made of fused silica is used. In this case, however, adsorption of the sample may prevent a good electroosmotic flow from being obtained. Accordingly, techniques of coating the inner walls of capillary tubes have been proposed (Patent Documents 1, 2, 3, and 4). On the other hand, hemoglobin (Hb) in blood reacts with glucose in the blood to become glycated Hb. The glycated Hb in the blood reflects the past history of the blood glucose level in a biological body and therefore is considered as an index in, for example, diagnosis and treatment of diabetes. Particularly, glycated beta chain N-terminal valine is called hemoglobin A1c (HbA1c) and is measured by, for example, a laboratory test, as an especially important index. Examples of the method of measuring hemoglobin in blood include an agarose electrophoresis method, a capillary electrophoresis method, an HPLC method, an immunization method, an enzymatic method, etc. Among these, those allowing minute variations such as hemoglobin variants to be detected are the capillary electrophoresis method and the HPLC method. On the other hand, an apparatus for analyzing hemoglobin is required to be reduced in size. With respect to this point, it is difficult to reduce the size of the whole apparatus in the HPLC method. On the other hand, the capillary electrophoresis method allows the size of the whole apparatus to be reduced, with the apparatus being formed into a microchip.
However, there is a problem in that the aforementioned conventional capillary electrophoresis method does not allow hemoglobin to be analyzed with high precision. In order to solve this problem, there is a technique in which the inner wall of a capillary tube is coated with a protein, which then is coated with polysaccharide (Patent Document 5). However, in this technique, an operation is required in which the inner wall of a capillary tube is coated with a protein each time the analysis is carried out, and therefore there is a problem in that the analysis becomes complicated. On the other hand, there is a method in which capillary electrophoresis is carried out with a zwitterionic type of running buffer that is allowed to contain a flow inhibitor such as aliphatic diamine, with the inner wall of the capillary tube not being coated (Patent Document 6). However, there is a problem in that this method allows variant hemoglobin to be separated but does not allow hemoglobin A1c to be separated. These problems apply to the general capillary electrophoresis method with respect to not only hemoglobin but also other samples.
[Patent Document 1] JP 2005-291926 A
[Patent Document 2] JP 4(1992)-320957 A
[Patent Document 3] JP 5(1993)-503989 A
[Patent Document 4] JP 8(1996)-504037 A
[Patent Document 5] JP 9(1997)-105739 A
[Patent Document 6] JP 2006-145537 A